Custom "point" mark shapes

[tuner]

This is a very low-priority issue.

Custom SVG shapes would be nice to have. Vega-Lite supports them in the shape property/channel through SVG path strings: https://vega.github.io/vega-lite/docs/point.html#properties

The custom paths could be rendered into an SDF texture, as shown in Ricky Reusser's sdf-points-with-regl notebook.
However, Ricky's notebook uses bitmap-sdf, which produces very low-quality SDFs, requiring very large texture sizes. Bitmap-sdf could be replaced with webgl-sdf-generator, which uses a different algorithm with a superior quality. Still, neither of them generates multichannel SDFs.

A significant limitation of SDF-based shapes is the rendering of strokes, which always have rounded joins, making shapes with sharp corners look quite silly:

To get sharp edges, pseudo distances (2.5 Pseudo-distance fields in Viktor Chlumský's thesis) could be used instead true distances. No JavaScript or WASM implementation exists, however.